High resolution ARPES measurements. High resolution angle-resolved photoemission measurements were carried out on our lab system equipped with a Scienta R8000 electron energy analyzer[1]}. We use helium discharge lamp as the light source which can provide photon energies of h\(\upsilon \) = 21.218 eV (helium I). The energy resolution was set at 4 meV for both the Fermi surface mapping and band structure measurements (Fig. 1 and Fig. 2) and for the superconducting gap measurements (Figs. 3 and 4). The angular resolution is \(\sim \) 0.3 degree. The Fermi level is referenced by measuring on a clean polycrystalline gold that is electrically connected to the sample. The sample was cleaved and measured in vacuum with a base pressure better than 5\(\times \) 10\(^{-11}\)  Torr.
